Air seeders and other seeding devices are commonly towed by tractors to apply seed or fertilizer, or both simultaneously, to a field. As an example, an air seeder may be towed in combination with a tilling implement, one behind the other, to place the seed and fertilizer under the surface of the soil. An air seeder has as its central component a wheeled seed cart which comprises one or more frame-mounted product tanks for holding product, generally seed or fertilizer or both. Air seeders also generally comprise a metering system for dispensing product from the tanks and a pneumatic distribution system for delivering the product from tank to soil.
It is known to provide an air seeder with volumetric meters which measure a fixed volume of seed per unit of linear distance. These volumetric meters typically comprise either augers or fluted cylinders (meter rollers) which rotate through a product reservoir to measure granular product, as illustrated in U.S. Pat Nos. 3,489,321 and 3,763,797. The meters rotate to feed product into a pneumatic distribution system. The pneumatic distribution system of an air seeder generally utilizes a centrifugal fan to provide at least one airstream which flows through the pneumatic distribution system to seed boots where product is deposited in the soil. Product is first introduced to the air stream by the metering system at a primary distribution manifold located below the metering system. Product is carried by the air stream through distribution lines to a series of secondary distribution manifolds ("headers"), which in turn distribute product through distribution lines to seed boots mounted behind ground openers on the tilling implement so that the product may be evenly delivered to the span of ground (the "tillage") acted upon by the tilling implement.
Operators of conventional seeding equipment often lose product to the tillage while the metering system is not operating, due to forces acting upon the product above the meter, including gravity and a lower pressure air stream running below the meter. The large central product tanks of an air seeder may lose substantial amount of product. One method of preventing lost product includes the use of a device to shut off flow of product between a product tank and a meter. For example, U.S. Pat No. 4,834,004 discloses slides which may be used to shut off product to a metering system. However, some amount of product may still be lost after the meter is shut off and before the shut-off device is actuated. In addition, operators must remember to actuate the shut-off device each time a meter is stopped.
In addition, if the product tank above the meter is not pressurized properly, the pressure in the product tank may be lower than the pressure of the air flowing through the pneumatic distribution system below the meter. In such a case, product may attempt to flow from the pneumatic distribution system through the meter and into the product tank, even while the meter is running. Even momentary occurrences of this condition can prevent product from flowing smoothly into the pneumatic distribution system and instead causes the product to bunch and pulse as it leaves the meter.
Therefore, it is desirable to devise a metering system having a mechanism to prevent air from the pneumatic distribution system from substantially affecting metering of product while the air flows through the metering system in reverse. It is also desirable to devise such a mechanism which may be replaced with relative ease.